This invention relates generally to thermal inkjet print heads. More particularly, the invention pertains to a thermal inkjet print head with resistance to organic solvents.
A known structure for interconnecting a thermal inkjet print head and its electrical components to a printing system controller is a tape automated bonded (TAB) interconnect circuit. TAB interconnect circuits used with thermal inkjet print heads are disclosed in U.S. Pat. Nos. 4,989,317; 4,944,850 and 5,748,209. A TAB circuit may be fabricated using a flexible polyimide substrate for supporting a metal conductor such as a gold plated copper. Known fabrication methods such as the “two layered process” or the “three layered process” may be used to create the components including device windows, contact pads and inner leads, for the TAB conductor circuit. In addition, a die-cut insulating film is applied to the conductor side of the TAB circuit to isolate the contact pads and traces from a cartridge housing on which the TAB circuit is affixed.
The print head is affixed to the TAB circuit in spaced relation to the contact pads, and the traces provide an electrical connection between the contact pads and the print head electrical components. When the TAB circuit, including the print head, is affixed to an inkjet cartridge, the print head portion of the TAB circuit is affixed to one side of the cartridge in fluid communication with an ink supply. That portion of the TAB having the contact pads is affixed to an adjacent side of the cartridge housing that is typically disposed perpendicular to the side of the cartridge housing to which the print head is attached. The contact pads are positioned on the cartridge housing for alignment with electrical leads on the printing system thereby electrically interconnecting the print head with a printing system controller to carry out print commands.
A typical thermal inkjet print head is essentially a silicon chip/substrate with thin-film structures such as an array of resistive heaters and corresponding transistors that switch the power pulses to the heaters. The print head may also include other components such as an identification circuit that provides coding information of print head characteristics and an electrostatic discharge component or electronic logics for multiplexing the firing of the heaters. After forming the film structures and circuits on the chip, an ink barrier layer is formed over the thin-film structures and etched or is otherwise treated to create a plurality of ink flow channels and ink chambers. Known ink flow channel and ink chamber architectures are disclosed in U.S. Pat. Nos. 4,794,410 and 4,882,595. In addition, an ink slot is formed by cutting a slot through a middle portion of the print head using known cutting techniques such as sand-blasting. This slot completes an ink flow network and places the print head in fluid communication with an ink supply.
A nozzle plate having a plurality of orifices is bonded to the ink barrier layer whereby each orifice is aligned with a corresponding ink chamber; and, for each ink chamber there is an associated heater and transistor. When power pulses are transmitted in accordance with print commands to the print head, the resistive heaters heat the ink in the ink chamber to create one or more pressure bubbles in the chamber that forces ink to eject in droplet form through respective orifices onto a print medium.
The resistive heaters and corresponding orifices in the nozzle plates have been arranged in at least two columns or rows depending on the orientation of the print head. The heaters and nozzles in a single row are offset relative to one another, and each of the columns is vertically or horizontally offset relative to one another. This type of arrangement of heaters and nozzles is used to minimize cross-talk between the heaters in a column, which may cause misfiring of ink drops. Multiplex drive circuits have been provided to control firing timing so that adjacent heaters in a column are not simultaneously fired to minimize cross-talking between fired heaters. Multiplexing may also reduce the number of signal lines in a circuit and the area required to complete the circuits, which area becomes a premium due to the crowding from other electrical components on a flex circuit.